Motor armature having distributed windings for reducing arcing
An armature for a brush commutated electric motor having a distributed coil winding arrangement for reducing brush arcing and electromagnetic interference (EMI). The winding pattern involves segmenting each coil into first and second subcoil portions with differing pluralities of turns. Each subcoil portion is wound around separate pairs of spaced apart slots of a lamination stack. Adjacent coils are wound such that one subcoil portion of each is wound in a common slot to therefore form an overlapping arrangement of each pair of adjacently coils. The winding pattern serves to “shift” the resultant magnetic axes of each coil in such a manner so as to significantly reduce brush arcing and the EMI resulting therefrom. The reduction in EMI is sufficient to eliminate the need for EMI reducing components, such as chokes, which have typically been required to maintain EMI to acceptably low levels. Commutation efficiency is also improved by the distributed winding pattern described above because of the reduction in the unevenness of the magnetic coupling between adjacent coils.
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This application is a continuation of U.S. Ser. No. 10/404,857, filed on Apr. 1, 2003 and presently, which is a divisional of U.S. Ser. No. 09/594,357, filed Jun. 14, 2000, which issued as U.S. Pat. No. 6,566,782 on May 20, 2003.
TECHNICAL FIELDThis invention relates to electric motors, and more particularly to a winding pattern for winding the coils on an armature in a manner to reduce electromagnetic interference and arcing at the brushes in contact with the commutator of the armature.
BACKGROUND OF THE INVENTIONPresent day brush commutated electric motors include an armature having a plurality of coils wound in slots formed in the lamination stack of the armature. With traditional motor designs, the lamination stack of the armature forms a plurality of circumferentially arranged slots extending between adjacent pairs of lamination posts. Typically, two coils per slot are used when winding the armature coils on the lamination stack. Among the two coils of the same slot, the one which commutates first is referred to as the first coil and the one which commutates second as the second coil. The second coil has inherently poorer magnetic commutation than the first coil because the second coil passes beyond the magnetic neutral zone within the stator before it finishes commutation. This is illustrated in simplified fashion in
Accordingly, it is a principal object of the present invention to provide an armature for a brush commutated electric motor having a plurality of coils wound thereon in a unique sequence which serves to significantly reduce brush arcing and improve the commutation efficiency of the motor.
It is a further object of the present invention to provide an armature for a brush commutated electric motor which incorporates a unique winding pattern for the coils wound on the armature in a manner which does not otherwise require modification of any component of the armature or the need for additional components.
It is still a further object of the present invention to provide a winding pattern for the armature coils of an armature which allows EMI components usually required to sufficiently attenuate the EMI generated by brush arcing to be eliminated, thus allowing the motor to be constructed less expensively and with fewer components.
SUMMARY OF THE INVENTIONThe above and other objects are provided by an armature for a brush commutated electric motor incorporating a unique, distributed winding pattern for the coils thereof, in accordance with a preferred embodiment of the present invention. The winding pattern involves segmenting each coil into first and second subcoil portions. With a first coil, the first subcoil portion is wound around two spaced apart slots for a first plurality of turns and the second subcoil portion is wound around a second pair of spaced apart slots which are shifted circumferentially from the first pair of slots. The second subcoil portion is also formed by a different plurality of winding turns than the first subcoil portion. The two subcoil portions are wound in series with one end coupled to a first commutator segment of the armature and the other end coupled to a second commutator segment.
A second coil is also divided into first and second subcoil portions, with the first subcoil portion being wound with the same number of turns as the second subcoil portion of the first coil, and in the second pair of spaced apart slots. The second subcoil portion of the second coil, however, is laterally shifted such that it is wound in a third pair of spaced apart slots shifted laterally by one slot from the second pair of slots. The second subcoil portion of the second coil is also wound a plurality of turns in accordance with that of the first portion of the first coil. One end of the first subcoil portion of the second coil is coupled to commutator segment number two while the end of subcoil portion two of coil two is coupled to commutator segment number three.
Coil number three is segmented into first and second subcoil portions with the first subcoil portion being wound a number of turns in accordance with the second subcoil portion of the second coil, and wound around the second pair of spaced apart slots. The second subcoil portion of the third coil is wound around the third pair of spaced apart slots but with a number of turns in accordance with the first subcoil portion of the second coil. The end of the first subcoil portion of the third coil is coupled to commutator segment number three while the end of the second subcoil portion of coil three is coupled to commutator segment number four.
The above winding pattern continues in alternating fashion such that an overlapping of the coils occurs around the lamination stack. In effect, all of the first subcoil portions shift their magnetic axes forward with respect to rotation of the armature, and all of the second coil portions shift their magnetic axes backward relative to the direction of armature rotation. With a desired turns ratio between the two subcoil portions of each coil, which ratio may vary considerably but is preferably about 3:1, the above described winding pattern smoothes out the “unevenness” in the magnetic coupling between adjacent armature coils, thus improving commutation efficiency. This also improves the commutation efficiency for the second subcoil portion of each coil, thus reducing brush arcing. This in turn serves to significantly reduce EMI. The reduction of EMI eliminates the need for expensive EMI suppression components that have previously been required for use with the motor brushes to ensure that EMI levels remain below regulated limits.
The various advantages of the present invention will become apparent to one skilled in the art by reading the following specification and subjoined claims and by referencing the following drawings in which:
Referring to
Referring to
Referring now to
Coil number 2 (252) also has a first subcoil portion 2A and a second subcoil 2B in series with one another. Subcoil portion 2A is wound in slots S1 and S6 with seventeen turns. Subcoil portion 2B is wound in series with portion 2A but around slots S5 and S7 of the lamination stack 14, and with seven winding turns. The end of subcoil portion 2A is coupled to commutator segment 122 while the end of subcoil portion 2B is coupled to commutator segment 123. The first subcoil portion 2A of coil 252 overlaps the second subcoil portion 1B of coil 251.
Coil number 3 (253) includes a first subcoil portion 3A and a second subcoil portion in series with one another 3B. Subcoil portion 3A is attached to commutator segment number 123 and includes seven winding turns wound around slots S1 and S6. Subcoil portion 3B is formed in series with subcoil portion 3A and includes seventeen turns wound in slots S2 and S7, with the end thereof being coupled to commutator segment 124.
Coil 4 (254) also includes a first subcoil portion 4A and a second subcoil portion 4B in series with subcoil portion 4A. Subcoil portion 4A has its end coupled to commutator segment 124 and includes seventeen turns wound around slots S2 and S7. Subcoil portion 4B includes seven turns wound around slots S3 and S8, with the end thereof being coupled to commutator segment 125. It will be noted that coil 254 partially overlaps coil 253. In effect, one of the subcoil portions of each adjacent pair of coils 25 overlap with each other.
The above-described pattern for coils 251-254 is repeated until all of the coils (in this example 24 coils) are wound onto the lamination stack 14. Each of the ends of the coils 251-2524 are further secured to immediately adjacent pairs of commutator segments 121-1224. For example, coil 255 has its ends secured to commutator segments 125 and 126, coil 256 to segments 126 and 127, and so forth.
The above-described winding pattern significantly improves the commutation performance of all of the second coil portions of the coils 25. Splitting each coil 25 into first and second subcoil portions allows each first subcoil portion to shift its magnetic axis away (i.e., laterally), from the position it would have otherwise had in a traditional two-coil-per-slot. This is illustrated in
In
In
Further, it can be seen by examining
The winding pattern employed on the armature 10 of the present invention also serves to significantly reduce the cost of constructing the armature by eliminating components that would otherwise be needed to sufficiently attenuate the EMI that results from traditional two-coil-per-slot winding patterns. Typically, inductive components are required to form a choke circuit associated with each armature brush. These additional components increase the overall cost of manufacturing a motor, as well as increase the complexity of the task of replacing the brushes during repair procedures.
The apparatus and method of the present invention thus allows an armature to be formed which significantly reduces brush arcing, and therefore the EMI that is present with traditional two-coil-per-slot armature constructions for all brush commutated electric motors. The apparatus and method of the present invention further does not increase the complexity of the manufacturing process or require additional component parts that would otherwise increase the overall cost of construction of an armature.
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.
Claims
1. An electric motor comprising:
- an armature having a plurality of spaced-apart posts defining a plurality of winding slots therebetween;
- a commutator having a plurality of commutator bars that number twice that of said winding slots;
- at least one brush disposed adjacent said commutator;
- a stator disposed coaxially with the armature, said stator having a plurality of spaced apart field coils;
- said armature including: a first coil having a first subcoil portion and a second subcoil portion having differing numbers of turns; said first subcoil portion being wound in a first pair of spaced apart ones of said slots; said second subcoil portion being wound in a second pair of spaced apart ones of said slots that are offset from said first pair of spaced apart slots; a second coil having a first subcoil portion and a second subcoil portion having differing numbers of turns; said first subcoil portion of said second coil being wound in said second pair of spaced apart slots so as to overlap said second subcoil portion of said first coil; said second subcoil portion of said second coil being wound in a third pair of spaced apart ones of said slots offset from said second pair of spaced apart slots; wherein both of said coils begin commutation at the same angular position relative to said brush; and wherein both of said coils end commutation at the same angular position relative to said brush.
2. The electric motor of claim 1, wherein one of said first and second subcoil portions of said first coil has approximately three times a number of winding turns as the other.
3. The electric motor of claim 1, further comprising a third coil having first and second subcoil portions that are wound in the same said slots as said subcoil portions of said second coil.
4. An electric motor having an armature, the electric motor comprising:
- a lamination stack having a plurality of radially extending posts, said posts forming a plurality of slots therebetween, said slots being arranged in a circumferential pattern;
- a plurality of coils wound around said slots, said coils being arranged in pairs about said lamination stack;
- each said coil being divided into first and second subcoil portions, with said first subcoil portion having a first plurality of winding turns and said second subcoil portion having a second plurality of winding turns, and wherein said first and second subcoil portions are wound in different, circumferentially offset pairs of said slots and coupled to designated pairs of commutator segments of a commutator;
- wherein a first pair of said coils are wound in an overlapping fashion such that the first subcoil portion of a second one of said first pair of coils is wound in the same slots as said second subcoil portion of a first one of said first pair of coils, and said second subsoil portion of said second one of said first pair of coils is wound in a pair of slots offset by one slot position from said slots that said second subcoil portion of said first one of said first pair of coils is wound in; and
- wherein a second pair of coils circumferentially offset from said first pair of coils is further wound such that a first subsoil portion of a first one of said second pair of coils is wound in the same slots as said first subcoil portion of said second coil of said first pair of coils, and said second subcoil portion of said first one of said second one of second pair of coils is wound in the same slots as said second subsoil portion of said second coil of said first pair of coils; and
- wherein a resultant magnetic axis of each said coil is at the same angular position relative to the pair of commutator segments to which each said coil is secured; and
- wherein said same angular position enables coincident commutation zones to be formed for each of said coils.
5. The electric motor of claim 4, wherein one of said first and second subcoil portions of each said coil has a greater number of winding turns that the other of said subcoil portions.
6. The electric motor of claim 4, wherein one of said first and second subcoil portions of each said coil has approximately three times the number of winding turns as the other of said subcoil portions.
7. An electric, rotating machine comprising:
- a stator having a plurality of field coils, wherein said field coils are spaced apart to form gaps therebetween;
- an armature having a plurality of coils wound thereon such that a magnetic axis of a first one of said coils is advanced, relative to a given pair of said field coils when said first coil is excited, and a magnetic axis of a second one of said coils is retarded, relative to said given pair of field coils when said second coil is excited; and
- wherein said first and second coils complete commutation while passing through coincident angular regions relative to said brush.
8. The machine of claim 7, wherein each of said first and second coils is segmented into two subcoil portions coupled in series.
9. The machine of claim 8, wherein said subcoil portions of said first and second coils are wound such that at least one of said subcoil portions of each are wound in a common pair of slots of said armature.
10. An electric motor comprising:
- an armature having a plurality of spaced apart posts defining a plurality of spaced apart winding slots;
- a stator disposed coaxially with the armature, said stator having a plurality of spaced apart field coils defining an angular region between each adjacent pair of said field coils;
- said armature including: a first coil having a first subcoil portion and a second subcoil portion; said first subcoil portion having a first plurality of winding turns and being wound in a first pair of spaced apart ones of said slots; said second subcoil portion having a second plurality of winding turns and being wound in a second pair of spaced apart ones of said slots that are offset from said first pair of spaced apart slots; a second coil having first and second subcoil portions wound in third and fourth pairs, respectively, of spaced apart ones of said slots; wherein said subcoils of said first coil are wound with different numbers of winding turns to shift a resultant magnetic axis of said first coil so that said resultant magnetic axis lies at a first predetermined angular position relative to a first pair of commutator bar to which said first coil is secured; wherein said subcoils of said second coil are wound with differing numbers of turns to align a resultant magnetic axis of said second coil at a second predetermined angular position to a second pair of commutator bars to which said second coil is secured; and wherein said first and second predetermined angular positions define the same angular position, and wherein said coils have coincident commutation regions.
11. An electric motor of claim 10, wherein said subcoil portions of each said coil have differing numbers of winding turns.
12. An electric motor comprising:
- an armature having a plurality of spaced apart posts defining a plurality of spaced apart winding slots;
- a stator disposed coaxially with the armature, said stator having a plurality of spaced apart field coils defining an angular region between each adjacent pair of said field coils;
- said armature including: a first coil having a first subcoil portion and a second subcoil portion; said first subcoil portion having a first plurality of winding turns and being wound in a first pair of spaced apart ones of said slots; said second subcoil portion having a second plurality of winding turns and being wound in a second pair of spaced apart ones of said slots that are offset from said first pair of spaced apart slots; a second coil having first and second subcoil portions wound in third and fourth pairs, respectively, of spaced apart ones of said slots; wherein a resultant magnetic axis of said first coil is positioned at a first angular point relative to a pair of commutator bars to which said first coil is coupled; wherein a resultant magnetic axis of said second coil is positioned at a second angular point relative to a pair of commutator bars to which said second coil is coupled, said first and second angular points defining the same angular point; and wherein both of said coils begin and complete commutation within a predetermined, coincident angular commutation region relative to said given pair of field coils.
13. The electric motor of claim 12, wherein said first and second subcoil portions of each of said first and second coils are wound with differing numbers of winding turns.
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Type: Grant
Filed: Jul 3, 2003
Date of Patent: Aug 16, 2005
Patent Publication Number: 20040017124
Assignee: Black & Decker Inc. (Newark, DE)
Inventor: Ren Hong Wang (Timonium, MD)
Primary Examiner: Karl I. E. Tamai
Attorney: Harness, Dickey & Pierce, P.L.C.
Application Number: 10/613,187